On-vehicle disk brake lathes are employed to periodically resurface disk brake rotors to assure proper functioning of the vehicle brakes, and allow the brake disk to be machined without removal from the wheel hub to which the brake disk is mounted. To assure that lateral runout of the disk is reduced sufficiently to meet vehicle specifications, the lathe has an alignment mechanism to substantially align a rotational axis of the lathe with the axis of rotation of the wheel hub on which the brake disk is mounted. Since the lathe machines the surfaces of the brake disk along a path normal to the lathe axis, misalignment of the lathe axis with the axis of rotation introduces undesirable lateral runout in the machined brake disk when rotated about the wheel hub axis; thus, the misalignment of these axes should be reduced to be sufficiently small that the resulting lateral runout of the machined disk is within the manufacturer's specifications. Currently, two approaches have been taken to automatically reduce the misalignment between the lathe axis and the hub axis.
U.S. Pat. No. 6,101,911 teaches a trial-and-error approach for adjusting an alignment mechanism, where the positions of a pair of opposed slant disks are incrementally adjusted to change the magnitude and orientation of the angle between the hub axis and the lathe axis. An alignment signal generated by a rotational accelerometer is monitored to see whether each change reduces or increases the misalignment. If the change increases the misalignment, then the change is reversed and either a countering change made or, if that particular disk movement has already been adjusted, then the other disk position is adjusted. This trial-end-error adjustment is continued until such time as the alignment signal reaches a signal level that is consistent with an acceptable degree of lateral runout in the brake disk. If such a level cannot be achieved after a specified time period or after a specified number of attempts, then a notice of such condition is provided to the operator.
An alternative approach is taught in U.S. Pat. No. 6,813,979, where the lateral runout due to misalignment is measured and an adjustment to correct the misalignment is calculated based on the lateral runout measurement. The adjustment is automatically performed by adjusting the relative extensions of three radially-arranged adjustment elements interposed between two disks. To measure the lateral runout used to calculate the needed adjustment, the '979 patent employs a feeler-type probe which is taught as providing an authentic representation of lateral runout to overcome some of the problems pointed out with the use of indirect measurement, such as by use of an accelerometer as taught in the '911 patent.